Background: The medial aspect of the knee has a complex capsular structure; the biomechanical roles of specific structures are not well understood. Hypothesis: The 3 strong stabilizing structures, the superficial and deep medial collateral ligaments and the posteromedial capsule, make distinct contributions to controlling tibiofemoral laxity. Study Design: Controlled laboratory study. Methods: Changes in knee laxity under anterior-posterior drawer, valgus, and internal-external rotation loads were found by sequential cutting in 18 cadaveric knees. Three cutting sequences allowed the roles of the 3 structures to be seen in isolation and in combination. Some force contributions were also calculated. Results: The posteromedial capsule controlled valgus, internal rotation, and posterior drawer in extension, resisting 42% of a 150-N drawer force when the tibia was in internal rotation. The superficial collateral ligament controlled valgus at all angles and was dominant from 30° to 90° of flexion, plus internal rotation in flexion. The deep collateral ligament controlled tibial anterior drawer of the flexed and externally rotated knee and was a secondary restraint to valgus. Conclusion: Distinct roles in controlling tibiofemoral laxity have been found for these structures that vary according to knee flexion and tibial rotation. Clinical Relevance: The restraining functions demonstrated provide new information about knee stabilization, which may allow better evaluation of structural damage at the medial aspect of the knee.

Background: The optimal method for arthroscopic rotator cuff repair is not yet known. The hypothesis of the present study was that a double-row repair would demonstrate superior static and cyclic mechanical behavior when compared with a single-row repair. The specific aims were to measure gap formation at the bone-tendon interface under static creep loading and the ultimate strength and mode of failure of both methods of repair under cyclic loading. Methods: A standardized tear of the supraspinatus tendon was created in sixteen fresh cadaveric shoulders. Arthroscopic rotator cuff repairs were performed with use of either a double-row technique (eight specimens) or a single-row technique (eight specimens) with nonabsorbable sutures that were double-loaded on a titanium suture anchor. The repairs were loaded statically for one hour, and the gap formation was measured. Cyclic loading to failure was then performed. Results: Gap formation during static loading was significantly greater in the single-row group than in the double-row group (mean and standard deviation, 5.0 ± 1.2 mm compared with 3.8 ± 1.4 mm; p < 0.05). Under cyclic loading, the double-row repairs failed at a mean of 320 ± 96.9 N whereas the single-row repairs failed at a mean of 224 ± 147.9 N (p = 0.058). Three single-row repairs and three double-row repairs failed as a result of suture cut-through. Four single-row repairs and one double-row repair failed as a result of anchor or suture failure. The remaining five repairs did not fail, and a midsubstance tear of the tendon occurred. Conclusions: Although more technically demanding, the double-row technique demonstrates superior resistance to gap formation under static loading as compared with the single-row technique. Clinical Relevance: A double-row reconstruction of the supraspinatus tendon insertion may provide a more reliable construct than a single-row repair and could be used as an alternative to open reconstruction for the treatment of isolated tears.